The overall goal of this project is to characterize the expression of genes within hair follicle stem cells and to study the role of specific genes in maintaining the stem cell phenotype. The hair follicle is a model for studying epithelial stem cells and understanding the mechanisms which maintain the homeostasis of hair follicle stem cells and may lead to advances in the areas of tumorigenesis, wound healing and hair disorders. Similar to other self renewing tissues, such as bone marrow, gastrointestinal tract and epidermis, the hair follicle contains slowly cycling stem cells with a high proliferative capacity and the ability to produce differentiated cells to regenerate the tissue. Unlike other tissues, however, hair follicle growth (anagen) is interrupted by periods of regression (catagen) and rest (telogen), with subsequent regeneration. Since the lower follicle degenerates in the catagen phase, leaving only the telogen club structure, this residual epithelial cap surrounding the club hair represents an enriched source of stem cells which are responsible for regenerating a new lower follicle in anagen. They have extracted RNA from the stem cell rich area of telogen follicles as well as from the bulb area of anagen follicles dissected from human scalp. Through cDNA expression arrays, a number of genes appear to be expressed in the stem cell area that are not expressed in matrix keratinocytes of the anagen bulb. Several of the genes have been shown to mediate proliferative behavior and differentiation pathways in other experimental systems. The hypothesis that will be tested in this proposal is that specific genes expressed in the stem cells of the hair follicle are important in maintaining stem cell properties. The specific aims are: 1. To characterize the expression of specific genes identified by the expression array through in situ hybridization, immunohistochemistry and immunofluorescence with confocal microscopy. Three genes which likely have roles in maintaining stem cell properties will be examined. 2. To test the significance of these three genes in maintaining in vitro properties of hair follicle stem cells through retroviral transfection of human hair follicle stem cells with wild type and mutant gene constructs. Clonogenicity assays and other in vitro experiments of native and transfected stem cells will be used to study the role of these genes in clonality and other stem cell attributes. 3. To test the function of the specific genes during hair follicle development and cycling through in vitro and in vivo methods. Hair reconstitution assays performed with native and genetically altered stem cells will be used to analyze potential functions in folliculogenesis and cycling. In addition to the established mouse hair reconstitution system, they will attempt to develop a human hair follicle reconstitution system from hair follicle stem cells and microdissected dermal papillae using acellular dermal analogues with transplantation onto athymic mice.